Banana bunchy top disease, caused by Banana bunchy top virus (BBTV), is the most serious viral disease of banana worldwide. BBTV is the type-member of the Babuvirus genus in the family Nanoviridae and is a single-stranded (+) sense DNA virus with at least six genomic components that are each packaged in separate virions (Burns et al., “The Genome Organization of Banana Bunchy Top Virus: Analysis of Six ssDNA Components,” Journal of General Virology 76:1471-1482 (1995)). BBTV is transmitted within plantations by the banana aphid, Pentalonia nigronervosa, and is also transmitted through infected planting material (Magee, “Investigation on the Bunchy Top Disease of the Banana,” Council for Scientific and Industrial Research, Bulletin 30 (1927)). Infected plants become chlorotic and stunted. More importantly, plants infected prior to the initiation of flowering will not form fruits. Additionally, the virus spreads systemically to all plants in the mat resulting in nonproductive areas within plantations. Virus incidence may reach 100%, resulting in total yield loss and abandonment of fields.
BBTV was first detected in the State of Hawaii on the island of Oahu in 1989 (Ferreira, “The Status of Moko and Bunchy Top Diseases in Hawaii,” Research Ext. Service, CTAHR, UH Coop. Ext. Serv., Honolulu, Hi. (1991); Dietzgen et al., “Properties of Virus-like Particles Associated with Banana Bunchy Top Disease in Hawaii, Indonesia and Tonga,” Australasia Plant Pathology 20:161-165 (1991)) and has since spread to the Kona area on Hawaii (1995), to Kauai (1997), to Maui (2002), and to the Hilo area on Hawaii (2003). Currently, BBTV is the limiting factor for banana production on the island of Oahu, and has the potential to destroy the banana industry in Hawaii.
Once BBTV is present in a plantation, it is very difficult to control. Control of the aphid vector using insecticides is expensive, has low efficiency, and poses environmental and health risks. Removal of infected mats is required to limit spread of the virus but requires identification of early symptoms as well as increased labor and chemical costs. Reliable, economical, and environmentally sound control strategies are needed for the efficient control of BBTV in Hawaii. Development of resistant varieties is an environmentally sound, economical, and effective way to control plant diseases. However, BBTV resistance has not been found in any Musa germplasm. Even with resistance available in the germplasm, traditional breeding for disease resistance in banana is exceptionally difficult since all cultivated varieties are sterile, seedless clones that are vegetatively propagated.
Advances in biotechnology have led to the successful development and commercial release of several virus resistant crops including papaya, squash, and tomato. Transformation of banana has been reported by Sagi et al., “Genetic Transformation of Banana and Plantain (Musa spp.) via Particle Bombardment,”Bio/tech 13:481-485 (1995); May et al., “Generation of Transgenic Banana (Musa acuminata) Plants via Agrobacterium-Mediated Transformation,” Bio/tech 13:486-492 (1995); Becker et al., “Genetic Transformation of Cavendish Banana (Musa spp. AAA group) cv ‘Grand Nain’ via Microprojectile Bombardment,” Plant Cell Rep. 19:229-234 (2000); and Ganaphthi et al., “Agrobacterium-mediated Transformation of Embryogenic Cell Suspensions of the Banana Cultivar Rasthali (AAB),” Plant Cell Rep. 20:157-162 (2001)).
Researchers have used both biolistic- and Agrobacterium-mediated methods to transform either meristematic regions or embryogenic tissues of banana. The major obstacle to the production of transgenic banana has been the regeneration of large numbers of wholly-transformed plants. One procedure involves using secondary embryogenesis that allows for the production and regeneration of large numbers of plants initiated from single cells which should be wholly transformed (Khalil et al., “Regeneration of Banana (Musa spp. AAB cv. Dwarf Brazilian) via Secondary Somatic Embryogenesis,” Plant Cell Rep. 20:1128-1134 (2002)).
The present invention is directed to overcoming these and other limitations in the art.